This application claims the priority benefit of Taiwan application serial no. 88222562, filed Dec. 18, 1999.
1. Field of Invention
The present invention relates to an installation for increasing a scanning range of a scanner. More particularly, the present invention relates to an installation for increasing a scanning range of a scanner along an axial direction of a light source.
2. Description of Related Art
In general, a scanning system can be roughly classified as a reflective type or a light-penetrating type. In the reflective scanning system, a document is placed over a transparent glass panel. Light from a light source travels through the transparent glass panel and hits the document. The light is reflected back from the document to reach an optical sensor after passing through a set of optical elements. The optical sensor, for example, can be a charge couple device (CCD) where a scan image is formed. In the light-passing scanning system, the document is also placed on top of a transparent glass panel. However, light from a light source has to pass through the document, the transparent glass panel and a set of optical elements before arriving at the optical sensor.
Hence, both the reflective and the transparent type of scanning system operate on similar principles. In the reflective scanning system, brightness variation of the reflected light from a document is gauged to form an image. On the other hand, in the transparency scanning system, brightness variation of light after passing through the document is gauged to form an image.
However, the brightness level along a conventional longitudinal lamp tube, in other words, along the light axis of a light source, is brightest in the middle and dimmer on either side. Hence, the image produced by the light source will also be brighter in the middle than either side. Since a scanner works according to variation in brightness level, capacity for detecting brightness contrast near the two end sections of the light axis is lower. If the variation in brightness level along the axial direction of the light source is large, quality of a scan image near the edges of the light axis may deteriorate. Therefore, variation of brightness level along the light axis of a light source is an important parameter in document scanning.
In brief, the lesser the variation of brightness level along the light axis, the better will be the scanning range of the light source and the effective contrast of the document.
Accordingly, one object of the present invention is to provide an installation for increasing the scanning range along the axial direction of a light source. The installation is capable of increasing the usable range of a light source (or lamp tubes) and reducing spatial occupation of the scanner. In addition, the installation is able to resolve the problem of insufficient contrast near the side edges compared with the central area of a document.
In Taiwan Patent No. 352886 titled xe2x80x98A lens structure and its integration with an image-reading devicexe2x80x99, brightness variation along the axial direction of a light source is reduced by modifying a component. In the proposed device, a plurality of reflecting mirrors having coatings of varying thickness across the mirror surface is used inside the scanner. For example, the coating on the reflecting mirrors used for reflecting light is thickened in the middle or the coating thickness is reduced on each side of the reflecting mirrors so that brightness level through these mirrors are modified.
In this invention, rather than changing the reflectivity of the reflecting mirrors as in Taiwan Patent No. 352886, the transparent glass panel between the light source and a document or the transparency of glass panel that supports the document is modified.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an installation for increasing the scanning range along the axial direction of a light source. The installation includes a light source and a transparent glass panel. The light source provides a necessary beam of light for image scanning by the scanner. The transparent glass panel holds a scan document. Light from the light source penetrates the transparent glass panel and then passes through the document to produce a scan image. Alternatively, the light that penetrates the transparent glass panel is reflected back by the document to produce a scan image.
The transparent glass panel has a coating such that light transparency near the middle portion of the light axis is lower than near either end of the light axis.
This invention also provides a second installation for increasing the scanning range along the axial direction of a light source that includes a light source and a transparent glass panel. The light source provides a necessary beam of light for scanning a document by the scanner. The transparent glass is positioned between the light source and the scan document. Light from the light source penetrates the transparent glass panel and then impinges on the document for generating a scan image.
The transparent glass panel has a coating such that light transparency near the middle portion of the light axis is lower than at either end of the light axis.
Through the variation of light transparency across the transparent glass panel, this invention is able to smooth out the variation of brightness level along the light axis of the light source. Hence, scanning range of the light source is increased. Furthermore, since the variation of brightness level between the mid-portion and the sides is reduced, the problem of insufficient contrast near the edge compared with the central portion of a document is resolved.
In brief, this invention homogenizes the brightness level along the light axis by changing the light transparency across the surface of the light-channeling panel.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.